1. Field of the Invention
The present invention generally relates to a rolling bearing assembly adapted to prevent electrocorrosion due to an electric current flowing in rolling bearings utilized in a general purpose motor, an electric power generator or a traction motor of railway.
2. Description of the Conventional Art
Electrocorrosion preventive rolling bearing assemblies have been well known in the art and are disclosed in, for example, the Japanese Laid-open Patent Publication No. 2002-48145 and the Japanese Laid-open Utility Model Publication No. 2-46119. According to these publications, an electrocorrosion preventive rolling bearing assembly has an insulating layer formed by the use of a thermal spraying technique. The electrocorrosion preventive rolling bearing assembly having the insulating layer includes raceway members of which outer peripheral surfaces and annular end faces are covered by a metallic layer and an insulating layer.
In the case of the structure in which the insulating layer is formed, it appears that the difference in thickness of the insulating layer at the annular end faces may increase at the time of finishing work unless the thickness of the insulating layer is controlled and, hence, the insulating property may decrease consequently. When it comes to the thickness control of an insulating layer, thickness control of an insulating layer at the annular end faces of the deep groove ball bearing assembly has to be generally on the basis of raceway grooves and, on the other hand, such thickness control of the insulating layer at the annular end faces of the cylindrical roller bearing assembly has to be generally performed on the basis of rib surfaces of raceway members. Accordingly, not only are complicated work procedures required with a considerable length of time for complete measurements, but also since the end face machining work results in poor precision when performed directly on the basis of the raceway grooves or the ribs, a substantial amount of time and labor is required in accomplishing the work, thereby posing a problem associated with increase of the manufacturing cost.
Also, for mounting the outer race onto a housing by means of a crimping technique, a finishing work of the outer periphery of the outer race is generally carried out on the basis of the inner peripheral surface of the outer race as discussed below where the outer peripheral surface of the outer race that is covered by an electrically insulating layer requires the finishing work. Specifically, with reference to FIG. 9, this finishing work is carried out by fixing a tapered mandrel 36 along the inner peripheral surface of the outer race 32 and, then, while the outer race 32 is rotated together with the tapered mandrel 36, the outer peripheral surface of the outer race 32 is machined, for example, ground to the required dimension.
However, since the inner peripheral surface of the outer race of the bearing assembly is generally of a cylindrical shape, the machining technique shown in and described with reference to FIG. 9 has a problem in that even though the inner periphery of the outer race 32 is fixed at one end thereof to the tapered mandrel 36, a gap is naturally formed at the opposite end of the outer race 32 between the latter and the tapered mandrel 36. Because of this, there is a high possibility that during the machining the outer race 32 may be displaced and/or inclined relative to the tapered mandrel 36. Also, considering that the outer race 32 undergoes a thermal expansion by the effect of heat evolved during the machining, displacement and/or inclination of the outer race 32 relative to the tapered mandrel 36 are apt to occur more often than at normal temperatures. Once the displacement and/or inclination of the outer race 32 occur during the machining, it leads to poor precision (roundness, slant of the outer peripheral surface, radial deflection and so on) of the outer peripheral surface of the outer race 32. In order to alleviate these problems, the machining is typically performed while the outer race 32 is restrained, requiring further complicated work procedures.